A malfunctioning target drone, combined with judgment errors aboard the Navy cruiser Chancellorsville and at a Ventura County control center, led to the Nov. 13 accident that injured two sailors and breached the warship's hull.

A newly unclassified Navy report on the incident recommends administrative action against the ship's then-skipper, Capt. Andrew Hesser, and three key crew members for allowing a BQM-74 target drone to crash into the side of their ship without putting up an effective defense.

The repairs cost the Navy an estimated $30 million and took the ship out of service for a time. The drone's impact caused a fire in the breached space and in a portion of the electrical system. The report describes the sailors' injuries as minor.

The San Diego-based Chancellorsville was off the coast of Southern California in the middle of qualification trials for an upgrade to its Aegis-radar weapons system when the accident happened.

The drone was mimicking an incoming missile or similar kind of threat to the ship.

A Navy spokesman wouldn't say what kind of administrative action was taken against Hesser. Administrative actions can include a letter of caution or a formal counseling from a senior officer. They are not necessarily career enders.

Hesser served out his regular term aboard the Chancellorsville and is now working in a staff position at the Coronado-based Naval Surface Forces command.

Pacific Fleet commander Adm. Harry Harris had stern words for both the ship's skipper and the crew controlling the drone from Ventura's Point Mugu naval base.

“In the naval profession, we expect and trust our commanding officers to execute their duties with the utmost attention to detail, and we hold them accountable when they fail,” Harris wrote in the report.

“Likewise, we must set the conditions for success with our supporting actions. In this case, the personnel and systems designed to support and execute this complex test of Chancellorsville's combat system failed. Multiple indicators of control system anomalies were discounted or ignored. The control team failed to present a safe target profile to Chancellorsville and in so doing, put the ship at risk.”

U-T San Diego received a redacted copy of the formerly secret report after filing a Freedom of Information Act request.

A breakdown of the missteps:

• The target drone's control system failed, causing it to ignore the “turn away” command given by the Point Mugu control room.

• The operator of the ship's Close-In Weapons System – a warship's last line of defense against incoming missiles – received a “recommend fire” alert at his console, and reported it verbally. The ship's air warfare coordinator – one of three people on the ship with the authority to engage weapons – heard but did not act on the alert.

• The Point Mugu control room did not immediately call "rogue drone" when the drone failed to turn away a little more than 2 nautical miles from the ship. Sailors relied upon this "rogue drone" call. Not hearing the call, they did nothing to protect the ship, the report said.

• The team at Point Mugu knew the drone control system had failed or showed glitches several times that day, but they didn't stop the exercise or even tell the ship. “I question this control team's ability to continue to adequately service Pacific Fleet ships,” Harris said in his comments.

• The ship's combat systems coordinator changed the protocol for automatically activating the Chancellorsville's surface missile tracking system – without telling the skipper. The crew expected the missile system to track the drone and “were distracted attempting to conduct manual (tracking) while the drone continued inbound.”